For the past few years, Apple has made early versions of its operating systems available to those willing to brave the bugs. Through its beta software program, anyone willing to deal with spotty battery life or a crash or three could load up pre-release builds of iOS, macOS, watchOS or tvOS.

Ever wonder how many actually take advantage of it?

According to Tim Cook on today’s earnings call, more than four million people are currently running on the betas.

Alas, that’s as detailed as he got. He didn’t break down which platforms had the most beta users (though I’d bet iOS or macOS lead the way), nor what percentage of that beta group was developers (accessing the beta to debug their apps before the update) versus consumers (who just want to poke around the new goods early).

For reference: As of February of 2018, Apple had 1.3 billion active devices across Apple TV, iPhone, iPod Touch, iPad and Mac. So if each of the users Tim Cook mentioned is running a beta OS on one device, that’s around 0.3 percent of active devices running on a beta.

While that percentage might not sound huge, having four million people happily stress test your software before you officially ship it is a rare strength that few other companies can claim. Still, Apple has had a few rather glaring bugs slip through the cracks — from the annoying but forgettable bug that borked the letter “i” in iOS for a few days, to more severe security issues like the root user bug discovered in macOS at the end of last year. Could Apple be doing more to encourage pre-release bug hunting?